Method of increasing the volume yield of exfoliated vermiculite

ABSTRACT

A method is disclosed for increasing the volume yield of expanded vermiculite obtained by exfoliation of vermiculite ore particles. The method comprises the sequential steps of applying vegetable oil to the vermiculite ore particles and thermally exfoliating the vermiculite ore particles.

The present invention relates to the exfoliation of vermiculite ore andmore particularly to a method whereby the volume increase uponexfoliation of the vermiculite ore can be increased.

Vermiculite ore is well known for its capacity to undergo expansion toseveral times its original volume when subjected to elevatedtemperatures. The process of expanding vermiculite ore by heating isreferred to as thermal exfoliation. This process is generally acontinuous procedure in which vermiculite ore particles are fed into anexpansion kiln or oven, heated rapidly to temperatures in the range of1100° F. to 1900° F., and the resultant expanded vermiculite productremoved from the heating zone as additional unexpanded material isintroduced. The expanded vermiculite has a wide variety of well knownuses, including use as an aggregate in plaster and concreteformulations, a thermal insulator, an extender in fertilizers and soilmixes, an inert carrier for chemicals, a packaging material, and asroughage or filler in animal feeds.

In reference to thermal exfoliation of vermiculite, it is common in theart to refer to the "yield" obtained by exfoliation, this being thevolume of expanded vermiculite, when loosely accumulated withoutcompression of the expanded particles, obtained from an initial weightof unexpanded ore. Since expanded vermiculite is generally sold on avolume basis, it proves economically advantageous to the producer tomaximize the yield.

The present invention is directed toward a method for significantlyincreasing the yield of expanded vermiculite obtained by exfoliation ofvermiculite ore. The method of this invention comprises the steps ofapplying a vegetable oil to unexpanded vermiculite ore particles andthermally exfoliating the ore to which the oil has been applied. It hasbeen discovered that volume yield increases of up to about 9% can beattained with the present method. Volume yield increases in the range ofabout 4% to 7% are normally attained, although this range may vary as afunction of the particular oil, water content of the vermiculite, andthe origin of the vermiculite ore. As specified hereinafter, the yieldincreases are obtained with the application of relatively smallquantities of vegetable oil, thus making the present method economicallyattractive.

In accordance with the present method, the vegetable oil should beuniformly applied to the vermiculite ore so as to provide anapproximately equal amount of oil on each particle. This can beconveniently and accurately controlled by spraying the oil onto the oreparticles and agitating or tumbling the particles as the oil is applied.Spraying a fine mist of the oil onto the particles as they are tumbledin a rotating mixer such as a cannister, drum or paddle blender is thepreferred method. Spray application also facilitates modulation of thequantity of oil applied, so as to provide the desired uniformapplication using a minimal quantity of oil.

The oil is normally applied at ambient temperature, although it may beapplied at elevated temperatures, e.g., by pre-heating the oil or byapplying the oil to the vermiculite in a heated environment. Elevatedtemperatures may be advantageous, for example, for purposes of loweringthe viscosity of the oil and thereby facilitating the spraying processor the distribution of the oil on the ore particles. The elevatedtemperature should, however, be substantially below that at which thevermiculite undergoes exfoliation, inasmuch as the oil or, morespecifically, the oil temperature is not used to expand or promoteexpansion of the vermiculite.

The vegetable oil can be applied to the vermiculite in any amount whichaffords a volume yield increase. In the general, the oil is applied in aweight percentage amount of at least about 0.1%, based on the weight ofvermiculite ore. Typically, the oil is applied in a weight percentagerange of about 0.1%, based on the weight of vermiculite ore. Thisrelatively small quantity of oil helps minimize any additional costincurred by use of the present method and, thus, contributessignificantly to the economic feasibility of employing the presentmethod.

Vegetable oils constitute a well known and widely used class ofmaterials. As used herein, the term "vegetable oil" includes all oilsderived from vegetable seeds, fruits, and other vegetable matter. Thevegetable oil can be refined or unrefined, unsaturated, or partially orcompletely hydrogenated. Examples of vegetable oils which can be usedherein are soybean oil, castor oil, corn oil, sunflower oil, palm oil,cottonseed oil, peanut oil, and olive oil. Vegetable oils containsubstantial levels of fatty acids and the present invention includes theuse of fatty acids, per se, derived from or extracted out of vegetableoils. The term "vegetable oil", as used herein, thus also includes fattyacids, per se, derived from vegetable oil, examples of which are oleicacid, linoleic acid, lauric acid, ricinoleic acid, stearic acid, andpalmitic acid.

The vermiculite ore to which the oil is applied should be dry to thetouch and free flowing. Most preferably, the ore should be dried toremove essentially all of the unbound or surface water which isinitially present on the ore sample. The ore should, however, retain itsbound interlayer water, generally constituting 5% to 10% by weight ofthe ore, this water being generally recognized in the art as necessaryfor optimal thermal expansion of the ore.

The vegetable oil is believed to form a coating on at least the exteriormajor surfaces of the vermiculite ore particles. Although not wishing tobe bound by any particular theory, it is speculated that this coating,due primarily to its hydrophobicity, inhibits the liberation of theinterlayer water from the particles during exfoliation and therebyprovides a greater degree of expansion of the individual particles andan overall increase in volume yield.

The ore particles used in the present process can be of any convenientdimension or size. As a general rule, vermiculite ore particles areobtained, either by milling or as naturally occurring materials, inparticle sizes measuring from about 0.005 in. up to about 0.4 in. acrosstheir surface. These particles can be segregated according to size byscreening, with arbitrary maximum and minimum sizes being set to definea given size range or grade of ore particles. After being separated intothe various size grades, the ore particles are thermally exfoliated toyield an expanded product of substantially uniform particle size. Inaccordance with the practice in the art, the present method is alsonormally conducted employing ore particles which fall within arelatively narrow size range, as opposed to a mixture of particles whichvary widely in size. As illustrated in the following Example, volumeyield increases were obtained in the exfoliation of all of the variouscommercial grades of vermiculite ore which were expanded in accordancewith the present method.

The oil treatment step of the present method provides an additionaladvantage in that it substantially reduces the dust which is oftengenerated in the transport and handling of vermiculite ore, i.e., theoil which is applied to the ore is able to bind substantially the dustand fibrous particles present in the ore and thus suppress theliberation of same during the handling of the ore. It has been foundthat the application of as little as 0.1% of oil can provide substantialdecreases in dust and fiber liberation and that the effectiveness of theoil in this respect increases with increasing dosage. From thestandpoint of health and safety, this dust suppression aspect of theinvention can be particularly advantageous and beneficial.

The oil treated vermiculite ore particles of this invention can bethermally exfoliated utilizing any of those procedures heretofore knownin the art. Any suitable vermiculite expansion oven or furnace may beused. Thermal exfoliation procedures generally involve the continuousintroduction of vermiculate ore particles into the upper end of a hightemperature oven or furnace, at which point the ore is exposed totemperatures in the range of about 1100° F. to 1900° F. and undergoesrapid expansion. The expanded ore is allowed to fall to a lower zonewithin the oven under the action of gravity, at which point theparticles may continue to expand due, at least in part, to residual heatacquired in the upper zone and retained in the particle. The particlesare withdrawn from the lower end of the furnace at a rate approximatelyequal to the introduction of new particles into the furnace. Vermiculiteexfoliation procedures and furnace apparatus for use in exfoliation aredisclosed in U.S. Pat. Nos. 2,203,821; 3,010,911; and 3,533,610, and thedisclosure of each of these patents is hereby incorporated by reference.

The present invention is further illustrated in the following Examplewhich is intended as illustrative only and not in any limiting sense.

EXAMPLE

Five different size commercial grades of vermiculite ore were eachdivided into fifty pound batches and each batch was treated with apredetermined amount of partially hydrogenated refined soybean oil. Eachoil application was conducted at ambient temperature by spraying a finemist of the oil onto the ore particles as the particles were tumbled ina rotating drum mixer. The oil was dispensed at a rate of about 300cc./min. over a period of 10 to 40 seconds, depending on the totalamount of oil to be applied. After the spray application was completed,tumbling of the ore was continued for approximately 10 minutes.

The five different grades of vermiculite ore used in this Example,designated herein as Ore Grades A through E, were all commercial gradeores obtained from a mine in Libby, Mont. Previous analyses of samplesof these commercial grades indicated the following bulk density andparticle size distribution ranges:

    ______________________________________                                        Sieve size    Weight Percent Retained                                         (U.S. Series) Max.      Min.                                                  ______________________________________                                        Ore Grade A:                                                                  Bulk density: 45-60 lbs./ft..sup.3                                             3/8          10        0                                                      4            35        10                                                     6            55        25                                                     8            35        15                                                    16             6        0                                                     30             6        0                                                     Ore Grade B:                                                                  Bulk density: 55-65 lbs./ft..sup.3                                             6            12        0                                                      8            40        25                                                    16            85        45                                                    30            10        0                                                     Ore Grade C:                                                                  Bulk density: 55-65 lbs./ft..sup.3                                             8             1        0                                                     16            38        10                                                    30            78        40                                                    50            15        5                                                     100           15        0                                                     >100           9        0                                                     Ore Grade D:                                                                  Bulk density: 55-65 lbs./ft..sup.3                                            30            27        5                                                     50            80        40                                                    100           30        5                                                     >100          10        6                                                     Ore Grade E:                                                                  Bulk density: 60-70 lbs./ft..sup.3                                            30             1        0                                                     50            18        0                                                     100           70        35                                                    >100          70        24                                                    ______________________________________                                    

Two hundred and fifty grams of each oil treated sample were expanded inan electrically heated laboratory assay furnace at a temperature ofapproximately 1800° F. The furnace comprised a four foot long columnequipped with internal baffles. The vermiculite ore was introduced atthe top of the column and allowed to fall under gravity through thebaffle system, this requiring approximately 10-15 seconds.

The expanded ore was collected at the bottom of the column, allowed tocool, and poured into a 5 liter graduated cylinder to determine thefinal volume. This volume was extrapolated to a "bag yield"corresponding to the number of 4 cubic foot bags which would be obtainedfrom one ton of the oil-heated ore sample. For comparison purposes, a"Control" sample of 250 grams of each ore grade, which was not treatedwith the oil, was expanded in an identical manner and the resultantvolume or extrapolated bag yield used as a basis for determining yieldincreases due to oil application. Table 1 provides the results for alltest and control samples. In Table 1, the "Oil Dosage" is the amount ofoil in ounces applied to each 50 pound ore sample.

                  TABLE 1                                                         ______________________________________                                                                Yield     % Yield                                     Ore Grade Oil Dosage (oz.)                                                                            (Bags/Ton)                                                                              Increase                                    ______________________________________                                        A         Control       95.5      --                                          A         0.8           95.5      0                                           A         1.6           98.2      2.8                                         A         2.4           98.2      2.8                                         A         3.2           100.9     5.6                                         B         Control       84.5      --                                          B         0.8           87.3      3.3                                         B         1.6           87.3      3.3                                         B         2.4           87.3      3.3                                         B         3.2           88.7      4.9                                         C         Control       75.8      --                                          C         0.8           83.7      10.4                                        C         1.6           82.3      8.5                                         C         2.4           82.3      8.5                                         C         3.2           82.3      8.5                                         D         Control       60.5      --                                          D         0.8           63.3      4.6                                         D         1.6           63.3      4.6                                         D         2.4           63.3      4.6                                         E         Control       44.9      --                                          E         3.2           47.6      6                                           E         4.0           47.6      6                                           E         4.8           47.6      6                                           ______________________________________                                    

Each of the above oil-treated samples was observed to generatesubstantially less dust during handling than did the control samples.

It should be appreciated that the results provided in Table 1 areillustrative and that the volume yield increases may vary depending on,for example, the oil applied to the ore, ore content and origin, andexpansion temperatures and procedures. In addition, since certainchanges, modifications, and substitutions can be made in theabove-described method without departing from the scope of theinvention, it is intended that all matter contained in the abovedescription shall be interpreted as illustrative and not limitative.

What is claimed is:
 1. A method for increasing the volume yield ofexpanded vermiculite ore particles comprising the sequential steps ofapplying about 0.1% to about 1% by weight of a vegetable oil to saidparticles, based on the weight of said particles, at a temperature belowthat at which said ore particles undergo exfoliation and thermallyexfoliating said ore particles in an expansion oven or expansionfurnace.
 2. A method of claim 1 wherein said vegetable oil is selectedfrom the group consisting of soybean oil, castor oil, corn oil,sunflower oil, palm oil, cottonseed oil, peanut oil, olive oil, andfatty acids derived therefrom.
 3. A method of claim 2 wherein saidvegetable oil is soybean oil.
 4. A method of claim 1 wherein saidvegetable oil is sprayed onto said particles as said particles aretumbled in a rotating mixer.
 5. A method of claim 1 wherein saidparticles are thermally exfoliated at a temperature in the range ofabout 1100° F. to 1900° F.